Branched aromatic polyesters and cross-linked derivatives thereof

ABSTRACT

M IS 0 OR 1; N IS 0 OR 1; A IS 0-40; B IS 0-20; C IS 0-20; AND A + B + C IS 2-40.   and wherein X is   vo wherein R1, R2 and R3 each consist essentially of a plurality of moieties selected from the group having the Formulas II, III and IV   Branched, wholly aromatic polyesters of Formula I

nited States Patent [191 Economy et a1.

1*Dec. 31, 1974 1 1 BRANCHED AROMATIC POLYESTERS AND CROSS-LINKEDDERIVATIVES THEREOF [75] Inventors: James Economy, Eggertsville; SteveG. Cottis, Amherst; Bernard E. Nowak, Lancaster, all of NY.

[73] Assignee: The Carborundum Company,

Niagara Falls, NY.

21 Appl. No.: 413,474

Related US. Application Data [62] Division of Ser. No. 96,234, Dec. 8,1970.

[52] US. Cl 260/47 CP, 117/161 K, 161/231, 260/4 XZ, 260/49, 260/248 SC,260/873 [51] Int. Cl C08g 17/02, C08g 17/08 [58] Field of Search 260/47CP, 47 CZ, 49

[56] References Cited UNlTED STATES PATENTS 3,047,532 7/1962 DAlelio260/45.4 3,050,496 8/1962 DAlelio 260/45.4 3,536,664 10/1970 Picklesimer260/47 3,637,595 1/1972 Cottis et a1. 260/47 3,772,250 11/1973 Economyet a1 260/47 CP Primary Examiner-Lester L. Lee Attorney, Agent, orFirmDavid E. Dougherty; Herbert W. Mylius [57] ABSTRACT Branched, whollyaromatic polyesters of Formula 1 wherein R, R and R" each consistessentially of a plurality of moieties selected from the group havingthe Formulas 11, Ill and 1V 1 law]- (III) and wherein X is 44 Claims, NoDrawings 96,234, filed Dec. 8, 1970.

This invention relates to polyesters, and more particularly to branchedpolyesters wherein branching occurs by virtue of a cyanuryl nucleus towhich linear polyester' chains are attached. Still more particularly,the novel branched polyesters of this invention are substantially whollyaromatic, that is, the linear polyester chains attached to the cyanurylnucleus consist solely of aromatic structural units, although the chainsmay in some instances terminate with an aliphatic end group. Theinvention further relates to methods for the preparation of suchbranched aromatic polyesters, to methods of curing and cross-linkingsuch polyesters, and to cured and cross-linked polyesters producedthereby.

Linear aromatic polyesters are well-known in the art. For example,linear polyesters consisting of repeating p-oxybenzoyl structural unitsin the polyester chain, sometimes termed p-oxybenzoyl homopolyesters,having been reported. Linear aromatic polyesters have also been reportedwhich consist of recurring, alternating structural units of two types inthe polyester chain: (l) isophthaloyl or terephthaloyl; and ('2) paraormeta- -dioxyphenylene. Both of these types of linear aromatic polyestersare highly advantageous in that they possess marked thermal stability,especially in contrast to linear polyesterswhich contain aliphatic aswell as aromatic structural units in the polymer chain. However, bothtypes also have serious disadvantages. For example, p-oxybenzoylhomopolyesters are difficult to fabricate into desired shapes by mostconventional methods because at high temperatures they tend to thermallydegrade rather than melt, and accordingly such conventional formingtechniques as casting, injection molding and extrusion are precluded.The same is true of the other aforementioned linear aromatic polyesters,especially if the structural units are of the para configuration, andwhile introduction of some structural units of the meta configurationmay improve fabricability, it does so at the expense of thermaldimensional stability.

The branched aromatic polyesters of the present invention represent asignificant advance over the prior art linear polyesters. In general,they possess the primary advantage of the linear aromatic polyesters,viz., outstanding thermal stability, while often being more easilyfabricable by virtue of a lower melting or softening point. Moreover,being branched, many polyesters of the invention lend themselves tocross-linking to produce polyesters having superior thermal properties,an advantage not generally possessed by linear polyesters.

According tothe present invention there are provided novel branched,wholly aromatic polyesters of Formula I wherein is a cyanuryl nucleusand wherein R, R and R each consist essentially of a plurality ofmoieties or strucitural units selected from the group having theFormulas II, III and IV a, b and 0 being integers representing the totalnumber of the respective moieties in each of R, R and R wherein x is nisO or 1 and when n is l, m is 0 or 1; a is an integer from 0 to about40; b is an integer from 0 to about 20', c is an integer from 0 to'about20; a b c is an integer from 2 to about 40; and the average value of a,b and c for R, R and R is from 2 to about 40. The carbonyl groups of themoiety of Formula II! are either para or meta to each other, as isconventionally indicated by the fact that the lines leading to the ringfrom the carbonyl groups intersect sides of the ring rather than beingconnected to specific apices thereof. Accordingly, the dicarbonyl moietyof Formula Ill is either isophthaloyl or terephthaloyl, or both withinthe same polyester chain. Similarly, the oxy groups of the moiety ofFormula IV are either para or meta to each other, as

is conventionally indicated, and accordingly the moiety of Formula IVmay be either metaor paradioxyarylene, or both within the same polyesterchain. When n is equal to l in Formula IV, para refers to the 4,4positions and meta refers to the" 3,4 or 3,3 positions. In thepolyesters of Formula I, the oxy groups of the moieties of Formulas IIand lVare linked to a carbonyl group of a moiety of Formulas II or IIIor to a carbon atom of the cyanuryl nucleus; the carbonyl groups of themoieties of Formulas II and III are linked to an oxy group of a moietyof Formulas II or IV; and thecarbon atoms of the cyanuryl nucleus arelinked to an oxy group of a moiety of Formulas II or IV. When a is O, bis an integer from l to about 20 and c is an integer from 1 to about 20.When b is 0, a is an integer from 1 to about 40 and c is or 1. when band c are each 0, a is an integer from 2 to about 40.

Preferably, n is equal to 0 in Formula IV, in which case the metaorpara-dioxyarylene moiety is metaor para-dioxyphenylene moiety of FormulaV I A l TU? wherein c has the same significance as described above. Itis also preferable that R, R and R each consist essentially of the sametypes of moieties, preferably in approximately the same proportions.

A particularly desirable type of branched aromatic polyesters of FormulaI consists of those polyesters containing the p-oxybenzoyl moiety ofFormula II, either with or without the additional presence of themoieties of Formulas III and IV; i.e., where a is an integer from 1 toabout 40.

It will be apparent that the number of moieties linked together to formthe polyester chains represented by R, R and R must be an integer, asrepresented by a, b and c. However, in many cases it is impractical oreven impossible with available analytical techniques to determine theprecise number of moieties in an individual polyester chain.Accordingly, the number of moieties in the polyester chains is oftenmore conveniently expressed as the average number of moieties in thethree chains, i.e., the average of a, b and c for R, R and R. In mostcases this average is determined as the average value of a, b and cfor'all of the molecules making up the particular batch of branchedpolyester being tested.

In accordance with the invention, low molecular weight branchedpolyesters may be produced having an average of from 2 to about moietiesor structural units in each polyester chain, corresponding to a molecular weight in the range from about 800 to about 2,300. Such branchedpolyesters are frequently referred to herein as prepolymers, and theirprincipal utility resides in the fact that their molecular weight may beincreased by cross-linking or by extending the length of the polyesterchains. Many of these prepolymers are fusible. They may be processedinto a desired physical form and subsequently advanced to a highmolecular weight polyester having outstanding thermal stability.

Higher molecular'weight branched polyesters may also be producedaccording to the invention. It appears that about 40 structural units isthe practical maximum number attainable in the polyester chains,corresponding to a maximum molecular weight from about 14,000 to about25,000. Many of these higher molecular weight polyesters having anaverage polyester chain length of more than about 10 structural units upto about 40 units ae useful as thermoplastic molding materials havingexcellent high temperature properties. They may be processed, forexample, by compression molding, impact moilding, ram extrusion orplasma spraying to make gaskets, bearing sleeves, protective coatings,electrical insulating coatings and the like. Many of the branchedpolyesters of the invention are also useful for the formation of filmsand fibers, as adhesives, and as matrices for fiber-reinforcedcomposites.

A variety of procedures and synthetic routes may be employed to producethe branched polyesters of the invention, and they are discussed indetail hereinafter. All involve a reaction or sequence of reactionsbetween suitable reactants which provide the cyanuryl nucleus and thedesired moieties of Formulas II, III and IV.

The cyanuryl nucleus is suitably provided by a cyanuric halide such ascyanuric bromide, cyanuric iodide, or

preferably cyanuric chloride, which is less expensive.

The p-oxybenzoyl moiety of Formula II is suitably provided by anycompound of Formula VI wherein R is lower alkanoyl, benzoyl, orpreferably hydrogen and R is hydrogen, lower alkyl, benzyl, phenyl, orphenyl wherein one or more hydrogens are replaced by halogen or loweralkyl, phenyl being preferred. The term lower as applied herein to alkyland alkanol refers to a content of from one to six carbon atoms. Examplsof compounds of Formula VI include, among others, p-hydroxybenzoic acid,phenyl phydroxybenzoate, p-acetoxybenzoic acid n-butyl pacetoxybenzoate,n-propyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, phenylp-acetoxybenzoate, phenyl p-benzoyloxybenzoate, benzylp-hydroxybenzoate, pcyclohexanecarbonyloxybenzoic acid, cresylphydroxybenzoate and m-chlorophenyl phydroxybenzoate. Phenylp-hydroxybenzoate is especially preferred, primarily because of itsthermal stability and reactivity.

The isophthaloyl or terephthaloyl moiety of Formula [II is suitablyprovided by isophthaloyl chloride or terephthaloyl chloride, or by anycompound of Formula VII 0 o R obU-bow phthalate, dicresyl terephthalate,di-p-chlorophenyl isophthalate and dicyclohexyl terephthalate. Diphenylisophthalate and diphenyl terephthalate are especially preferred becauseof their thermal stability and reactivy- The metaor para-dioxyarylenemoiety of Formula IV is suitably provided by any compound of FormulaVIlI (VIII) RQQZ QL n primarily because of their reactivity and/or lowercost.

The compounds of Formulas VI or VIII will react with a cyanuric halide,e.g., cyanuric chloride, whereby R, R or R combines with the halogen toproduce the corresponding halide as a by-product and whereby thep-oxybenzoyl moieties or dioxyarylene moieties are attached to thecarbon atoms of the cyanuric halide via ether linkages. It is by virtueof such reactions that branching is accomplished according to theinvention. Also, condensation reactions may occur as between R, R or Rand OR, OR or OR whereby the corresponding ester is produced as aby-product and the respective moieties link together via an esterlinkage. It is by virtue of such condensation reactions that polyesterchains are elaborated according to the invention. Esterester interchangemay, in some cases, occur as between polyester chains of differentmolecules, whereby the chain lengths and/or the order of the moieties inthe chains may be altered. It is apparent that each polyester chainattached to the cyanuryl nucleus will have a terminal group, theterminal group of a given polyester chain corresponding to the specificR, R R R, R or R present in the reactant selected. It is also apparentthat, as illustrated in the examples and described elsewhere herein,'thecomposition, number of structural units per chain, and molecular weightof the polyesters will depend not only upon the reactants selected, butupon the molar ratio thereof, in accordance with well-known principles.

Many of the desired reactions may be carried out most satisfactorily inthe molten state. Others are preferably carried out in any suitableliquid heat transfer medium, which may be a solvent for one or morereactants and/or reaction products, and which preferably has a highboiling point because some reactions are preferably carried out at arelatively high temperature. Numerous such liquids have been found to besuitable,

among which may be mentioned the terphenyls; a eu tectic mixture of73.5percent diphenyl oxide and 26.5percent diphenyl, commerciallyavailable under the trademark DOWTHERM A; mixtures of variouspolychlorinated biphenyls typified by those commercially available underthe trademark THERMINOL FR; polyaromatic ethers and mixtures thereofsuch as those composed in mixtures of meta and para isomers,havingboiling ranges in excess of 400C, typified by those commerciallyavailable under the trademark THER- MlNOl 77, and partially hydrogenatedterphenyls having boiling ranges in excess of 340C, typified by thosecommercially available under the trademark THER- MINOL 66.

One particularly desirable class of branched aromatic polyestersaccording to the invention comprises those polyesters of Formula Iwherein each chain attached to the cyanuryl nucleus (i.e., R, R and Rconsists essentially of repeating p-oxybenzoyl moieties of Formula II,the average number of structural units in each chain being from 2 toabout 40. Such polyesters correspond to Formula IX wherein d, e and findependently are integers from 2 to about 40 and the average of d, eand f is from 2 to about 40. Such polyesters may be readily prepared bythe reaction of cyanuric chloride with a compound of Formula VI andcondensation of the latter, as exemplified in Examples 1, 4 and 5. Theaverage length of the chains attached to the cyanuryl nucleus isgoverned by the molar proportions of the reactants. The p oxybenzoylchains terminate with a terminal group corresponding to R in Formula VI,thus these polyesters also correspond to Formula X r Wlii OL L Jrwherein d, e, f and R have the above-described meanings.

Example 1 illustrates the preparation of a prepolymer of this class ofbranched polyesters. The compound of Formula VI employed is thepreferred compound, phenyl p-hydroxybenzoate, conveniently prepared byreacting p-hydroxybenzoic acid with phenyl acetate in the presence ofHCl as a catalyst.

EXAMPLE 1 35.4 kg. (256.5 moles) of p-hydroxybenzoic acid and 43.6 kg.(320 moles) of phenyl acetate are placed into HCI inlet tube. Thereaction mixture is stirred constantly under a nitrogen atmospherethroughout the run. The reaction mixture is heated to C, forming a melt,and gaseous HCl is bubbled through the melt for 10.5 hours, thetemperature beingheld at 180C. Phe' nyl p-hydroxybenzoate is producedthereby, accompanied by distillation of acetic acid, the RC1 serving asa catalyst. The I-lCl flow is discontinued and the temperature of themelt is reduced to 170C, whereupon 8.27 kg. (44.8 moles) of cyanuricchloride is added. The temperature is held at 170C for 3.5 hours, thenincreased to C over a period of 2 hours. During this stage, some of thephenyl p-hydroxybenzoate reacts with all of the cyanuric chloride toproduce tris(p-carbophenoxyphenyl) cyanurate, accompanied by liberationof HCl. The temperature of the melt is then increased from 195to 250Cover a period of 7 hours and held at 250C for 4 hours. During thisstage, condensation occurs between the terminal phenoxy groups of thetris(p-carbophenoxyphenyl) cyanurate and the hydroxyl groups of theremaining phenyl phydroxybenzoate, accompanied by distillation of pheno]and excess phenyl acetate. The remaining melt is poured into trays andallowed to cool to room tempera ture (about 25C), solidifying. A yieldof 44 kg. is obtained. The product is pulverized, washed withtrichloroethylene and extracted with n-heptane in a Soxhlet extractor toremove any residual phenol and phenyl acetate, and dried in vacuum at110C for 2 hours. The product is a branched polyester prepolymercorresponding to Formulas IX and X wherein the average value of d, eandfis 2 and wherein R is phenyl. A substantial proportion of theproduct corresponds to Formulas IX and X wherein each of d, e and f is2. The product has a melting point of 350C as determined by differentialthermal analysis at a heating rate of 20C/minute. Saponification of theproduct and determination of the amount of phenol liberated indicates aphenyl terminal group content of 24.4 percent, corresponding closely tothe theoretical amount of 24.0 percent. The product contains 4.1 percentnitrogen.

Prepolymers such as that produced in Example 1 are fusible. They may beheated with a compound of Formula VI to extend the p-oxybenzoyl chainsand produce a branched, higher molecular weight polyester correspondingto Formulas IX and X with an average chain length of more than about upto about 40 poxybenzoyl units, such polyesters being useful, forexample, as thermoplastic molding compounds. This process is illustratedin Example 2. Such higher molecular weight polyesters may also beprepared directly, as illustrated in Examples 4 and 5.

Alternatively, prepolymers such as that produced in Example 1 may becured by cross-linking by heating with any suitable cross-linking agentat a temperature sufficiently high to cause cross-linking, to produce athermoset, cross-linked polyester having outstanding thermal stability.Such cross-linking is illustrated in Example 3. The cross-linkedpolyesters are useful, e.g., as adhesives, films, electrical insulationand the like. A

wide variety of substances may serve as suitable crosslinking agents,including, for example, aromatic dihydroxyl compounds such as resorcinoland hydroquinone; aromatic dicarboxylic acids such as isophthalic acidand terephthalic acid; and low molecular weight polyesters containingaromatic structural units derived from such dihydroxy compounds ordicarboxylic acids, such as employed in Example 3.

EXAMPLE 2 12 g. (about 0.01 mole) of the prepolymer powder produced inExample 1 and 214 g. (lmole) of phenyl p-hydroxybenzoate are slurried in400 g. of a polyaromatic ether heat transfer medium (b.p. above 400C).The mixture is heated, with stirring and under a nitrogen atmosphere,until a homogeneous liquid forms and further to 320C where thetemperature is held for 10 hours. During this time condensation occurs,accompanied by distillation of phenol, the p-oxybenzoyl chains of thebranched prepolymer are extended, and the resulting polyesterprecipitates. The reaction mixture is mixed with boiling acetone and thepolyester precipitate is removed by filtration, washed thoroughly withboiling acetone, and dried in air. A yield of 1 10 g. of polyesterpowder is obtained. The product is a branched polyester corresponding toFormulas [X and X wherein R is phenyl and the average value of d, eandfis about 30.

EXAMPLE 3 An aromatic polyester useful as a cross-linking agent for theprepolymer of Example 1 is produced as follows. 414 g. (3 moles) ofp-hydroxybenzoic acid, 510 g (3.75 moles) of phenyl acetate and 954 g.(3 moles) of diphenyl isophthalate are charged into a fournecked resinkettle equipped with a thermometer, stirrer, distilling head and acombination nitrogen-HCl inlet tube. The reaction mixture is stirredconstantly under a nitrogen atmosphere throughout the run. The reactionmixture is heated to 180C, and HCl is then bubbled through the mixturefor 7 hours, the temperature being held at 180C. Phenyl.p-hydroxybenzoate is thereby produced. The HCl flow is discontinued,the reaction mixture is heated to 200C at a rate of 10C/hour, 363 g.(3.3 moles) of hydroquinone is added, and the temperature is furtherincreased to 250C over a period of 2.5 hours..The distilling head isthen heated to C by external heating means to prevent condensation inthe distilling head of distillate subsequently to be produced. Thereaction 'mixture is heated to 320C over a period of 6 hours, held at320C for 16 hours, heated to 340C and held there for 3 hours. Duringthis stage, condensation occurs between the phenyl phydroxbenzoate,diphenyl isophthalate and hydroquinone, accompanied by the distillationof phenol. A total of 1,127 g. of distillate is collected during theentire run, the distillate containing acetic acid, phenol and the excessphenyl acetate.

The resulting melt is poured into a stainless steel tray and allowed tocool to room temperature, solidifying. The solid is ground to a powder.A yield of 1,037 g. (93 percent of theory) is obtained. The product is alinear copolyester having a low average molecular weight of about 3,600and consisting essentially of three types of moieties or structuralunits, viz., p-oxybenzoyl, isophthaloyl and p-dioxyphenylene. Thestructural units are joined to each other through ester linkages formingpolyester chains, which terminate with a hydroxyl group at each endbecause of the use of a molar excess of hydroquinone. The copolyestermolecules contain about 30 structural units on the average, some of themolecules having Formula XI and the others having Formula Xll (XII)wherein g and h are each about 10 on the average.

The linear copolyester is employed as a cross-linking agent instroke-curing a prepolymer of the invention as follows. 20 g. of thelinear copolyester is blended with 10 g. of the prepolymer powderproduced in Example 1 and the mixture is spread on the surface of a hotplate. The temperature of the hot plate is gradually increased. At about200C the mixture forms a clear melt, which is continually agitated witha spatula as the temperature continues to rise. When most of thevolatiles have been dissipated, agitation is discontinued and the meltis spread out into a film. As the temperature reaches about 270C, thematerial solidifies to form a thin, flexible film consisting essentiallyof thermoset cross-linked polyester. The cross-linking presumably occursinitially by virtue of condensation between the terminal hydroxyl groupsof the cross-linking agent and the terminal phenoxy groups of thebranched prepolymer, and subsequently by ester-ester interchangereactions. Various conventional techniques may be employed wherebycross-linking is effected to produce shaped bodies, fiber-reinforcedcomposites and the like.

EXAMPLE 4 414 g. (3 moles) of p-hydroxybenzoic acid, 510 g. (3.75 moles)of phenyl acetate and 1,000 g. of a partially hydrogenated terphenylheat transfer medium (boiling range 340396C) are charged into afournecked resin kettle equipped as in Example 3. The reaction mixtureis stirred constantly under a nitrogen atmosphere throughout the run.The reaction mixture is heated to 180Cand HCl is then bubbled throughthe mixture for 10 hours, the temperature being held at 180C. Thep-hydroxybenzoic acid is thereby converted to phenyl p-hydroxybenzoate,accompanied by distillation of acetic acid. The HCl flow isdiscontinued, the temperature is reduced to 170C, and 5.53 g. (0.03mole) of cyanuric chloride is added. The reaction mixture is held at170C for 8.5 hours, during which the cyanuric chloride reacts with asmall proportion of the phenyl p-hydroxybenzoate to producetris(p-carbophenoxyphenyl) cyanurate, accompanied by liberation of HCl.Virtually no condensation of the phenyl phydroxybenzoate occurs duringthis stage.

The temperature of the reaction mixture is increased from 170C to 320Cat a rate of 10C/hour and held at 320C for 5 hours. Meanwhile, thedistilling head is maintained at a temperature of 190C to preventcondensation of the distillate in the head. During this stage,condensation occurs as between the p-oxybenzoyl units attached to thecyanuryl nuclei and the phenyl phydroxybenzoate and/or autocondensationproducts thereof. chains of repeating p-oxybenzoyl units linked tocyanuryl nuclei thereby being elaborated. The condensation isaccompanied by distillation of phenol. The resulting branched polyesterforms a precipitate in the reaction mixture. A total of 589 g. ofdistillate containing acetic acid, phenol and the excess phenyl acetateis collected during the entire run.

The resulting polyester suspension is cooled to room temperature,congealing into a solid mass. The mass is extracted with acetone toremove the heat transfer medium and dried in vacuum. A yield of 330 g.(92.5 percent of theory) of polyester is obtained, the polyestercorresponding to Formulas IX and X wherein R is phenyl and the averageof d, e andfis about 30. The polyester is essentially the same as theone produced in Example 2. lsothermal gravimetric analysis in air at400C results in a weight loss of only 1.5percent/hour.

EXAMPLE 5 414 g. (3 moles) of p-hydroxybenzoic acid, 510 g.

- (3.75 moles) of phenyl acetate and 1,000 g. of a partiallyhydrogenated terphenyl heat transfer medium (boiling range 340396C) areplaced in a fournecked resin kettle equipped as in Example 3. Thereaction mixture is stirred constantly under a nitrogen atmospherethroughout the run. The reaction mixture is heated to 180C and HCl isthen bubbled through the mixture for 5 hours, the temperature being heldat 180C. The HCl flow is discontinued, the temperature is reduced to170C, 16.6 g. (0.09 mole) of cyanuric chloride is added, and thetemperature is held at 170C for 8.5 hours. The temperature is thengradually increased to 250C over a period of 5 hours, held at 250C for 2hours, gradually increased to 320C over a period of 6 hours, and held at320 C for 2 hours, the resulting polyester precipitating. A total of 595g. of distillate is collected during the entire run.

The polyester suspension is cooled to C, acetone is added, and thepolyester is recovered by filtration, washed with acetone, extractedwith acetone in a Soxhlet extractor, and dried in vacuum at 1 10C for 2hours. A yield of 325 g. (88 percent of theory) of polyester isobtained, the polyester corresponding to Formulas IX and X wherein R isphenyl and the average of d, e and f is about 11. The polyester tends toflow when subjected to a shearing force at about 200C. Isothermalgravimetric analysis in air at 400C results in a weight loss of only 1.9percent/hour.

Another particularly desirable class of branched aromatic polyestersaccording to the invention comprises those polyesters of Formula Iwherein each chain attached to the cyanuryl nucleus (i.e., R, R and Rconsists essentially of 1 metaor para-dioxyarylene moiety of Formula IVand from 1 to about 40 poxybenzoyl moieties of Formula II. Suchpolyesters are represented by Formula 1 wherein b is 0, c is l, and a isan integer from 1 to about 40.

One preferred embodiment of such polyesters contemplates a prepolymerhaving Formula X111 wherein X, m, n, R and R have the above-describedmeanings and R and R correspond to the particular R wherein X, m, n andR have the above-described meanings, R representing the terminal groups.Such prepolymers correspond to Formula I wherein b is 0, c is 1, and ais 2. They may readily be prepared by condensation of a compound ofFormula VI with a compound of Formula VIII in a molar ratio of 2:1 topro duce a linear polyester of Formula XIV wherein X, m, n and R havethe above-described meanings and R corresponds to the particular R groupof the compound of Formula VI employed, and then producing branching byreacting the linear polyester with cyanuric chloride in a molar ratio of3:1, as illustrated in Example 6.

A second preferred embodiment of this class of polyesters contemplates aprepolymer having Formula XV wherein R has Formula XVI (XVI) (XVII) andR groups of the reactants employed, and then producing branching byreacting the ester with cyanuric chloride in a molar ratio of 3:1, asillustrated in Example 7. It is apparent that R in Formula XVcorresponds to R or R in Formula XVII.

A third preferred embodiment contemplates reacting a prepolymer ofFormulas XIII or XV with a molar excess of a compound of Formula VIwhereby condensation occurs and the chains of the branched prepolymerare extended by the addition of repeating p-oxybenzoyl moieties. Thisextension of the chains is analogous to that illustrated in Example 2,and substantially the same conditions may be employed. The polyesters soproduced contain only one dioxyarylene moiety in each chain but maycontain up to about 40 p-oxybenzoyl units in each chain, depending uponthe molar ratio of the reactants.

-(3.48 moles) of p-hydroxybenzoic acid and 500 g. of a polyaromaticether heat transfer medium (b.p. above 400C) are placed in a four-neckedresin kettle equipped as in Example 3. The reaction mixture isconstantly stirred under a nitrogen atmosphere throughout the run. Thereaction mixture is heated to 180C, and gaseous I-lCl is then bubbledthrough the mixture as a catalyst for 5 hours, the temperature beingheld at 180C. The HCl flow is then discontinued. The mixture in theresin kettle at this point comprises a suspension of a linear polyesterhaving Formula XIV wherein R is hydrogen, n is 0, and the dioxyarylenemoiety is paradioxyphenylene. The polyester is formed by condensa- 'tionof the reactants, accompanied by distillation of acetic acid.

To the contents of the resin kettle are added 500 g. of the same heattransfer medium and 107.5 g (0.583 mole) of cyanuric chloride, and thetemperature of the reaction mixture is held at 180C for 8 hours. Duringthis stage the polyester reacts with the cyanuric chloride to produce abranched polyester prepolymer with the accompanying liberation of HClthe prepolymer being in suspension.

The mixture is cooled to C, acetone is added, and the mixture isfiltered to recover the product. The product is washed with acetone andis then subjected to extraction with acetone overnight in a Soxhletextractor. The produce is dried in vacuum at C for 2 hours.

A yield of 547 g. (83.8 percent of theory) of prepolymer powder isobtained. The prepolymer has Formula XIII wherein n is 0, R ishydrogenQand the dioxyarylene moieties are para-dioxyphenylene. Thepolyester powder forms a clear melt at a temperature of about 340C.

EXAMPLE '7 828 g. (6 moles) of p-hydroxybenzoic acid and 1,020 g. (6.5moles) of phenyl acetate are charged into a four-necked resin kettleequipped asin Example 3. The reaction mixture is stirredconstantly'under a nitrogen atmosphere throughout the run. The reactionmixture is heated to 180C, and gaseous l-ICl is then bubbled through themixture'for 7 hours, the temperature being held at 180C. Phenylp-hydroxybenzoate is produced thereby. The l-lCl flow is discontinuedand 660 g. (6 moles) of hydroquinone is added to the charge. Thedistilling head is heated to 180C, and the reaction mixture is heatedfrom 180 to 230C at a rate of 10C/hour, held for 4.5 hours at 230C, andheated to 240C where the temperature is held for 2 hours. The resultingpasty melt is poured while hot into a tray and allowed to cool andsolidify, whereupon it is pulverized. A yield of 1,413 g. is obtained.The product consists primarily of an ester, 7 p-llydroxyphenylphydroxybenzoate, having Formula XVII wherein R and R are each hydrogen,n is 0, and the dioxyarylene moiety is para-dioxyphenylene. The productalso contains a linear polyester identical to that produced in Example6. The desired ester is separable from the linear polyester by virtue ofits greater solubility in such so]- vents as acetone. Accordingly, theproduct is extracted with hot acetone to obtain a solution of the esterand in vacuum at 110C. The product is a branched polyester prepolymercorresponding to Formula XV wherein R is hydrogen and R has the FormulaXVI wherein n is 0 and the dioxyarylene moieties are paradioxyphenylene.

Prepolymers of Formula Xlll may be cured to produce very thermallystable thermoset polyesters. Such curing may be accomplished by heatingthe prepolymer above its melting point, as showni'n Example 8.

. EXAMPLE 8 5 g. of the branched polyester prepolymer prepared inExample 6 is placed on the surface of a hot plate at room temperatureand the temperature is gradually increased to 360C, the material meltingat about 340C. The material is spread out into a film and agitatedcontinuously with a spatula while the temperature is held at 360C. Afterabout minutes, the material is transformed into a powder as a result ofcuring, which presumably occurs by ester-ester interchange reactions.The product does not melt, but decomposes above 450C, and shows a weightloss in air at 400C of only 3 percent/hour. Analysis shows that theproduct contains 3.0 percent nitrogen.

Prepolymers of Formula XIII may also be cross linked by suspending theprepolymer in a suitable liquid heat transfer medium with cyanuricchloride as a cross-linking agent, preferably in an amount of aboutone-third mole per mole of prepolymer, and heating to a suitabletemperature, preferably at least about l-180C, whereby a cross-linkedpolyester is obtained which consists essentially of structural unitshaving Formula XVIII Qi Ql k3 1- water is added to the solution toprecipitate the ester, 50 wherein X, m and n have the above-describedmeanwhich is removed by filtration, dried in vacuum, and

crystallized from aqueous isopropyl alcohol. The ester is'found to havea melting point of 243C upon differential thermal analysis. v

460g. (2 moles) of the ester and 123 g. (0.67 mole) of cyanuric chlorideare suspended in 500 g. of a polyaromatic ether heat transfer medium(b.p. above 400C) in a four-necked resin kettle equipped as in Example3. The mixture is stirred constantly under a nitrogen atmospherethroughout the run. The mixture is heated to 180C, where the temperatureis held for 10 hours. During this period, the ester reacts with thecyanuric chloride to produce a branched polyester prepolymer, thereaction being accompanied by liberation of HCl. The reaction mixture iscooled to 80C and acetone is added thereto. The polyester product isrecovered by filtration, washed with acetone and then extracted withacetone in a Soxhlet extractor, and dried consisting essentially ofstructural units having Formula 15 16 wherein R has Formula XVI asdescribed above. ratio of about 1:111. Example 10 illustrates theprepara- Cross-linking the prepolymer of Example 7 in this mantion of alinear polyester which is branched to produce ner produces across-linked polyester consisting essena polyester according to theinvention, wherein the tially of structural units having Formula XIXwherein ratio of azbzc is about 8:1:1, the chains containing n is O andthe dioxyarylene moieties are parablocks of repeating p-oxybenzoylunits.

dioxyphenylene.

Another particularly desirable class of branched aro- EXAMPLE 9 maticpolyesters according to the invention comprises 103 (003 le) of thelinear copolyester those polyesters of Formula I wherein each chainatduced in Example 3 184 g. (00] mole) f cyanuric tached t0 the y ynucleus w R1, R2 and 10 chloride and 100 g. of a partially hydrogenatedtercontains at least one of each of the three moieties of h l heat t n fmedium (boiling range Formulas III and that is, a, b and C are each at340396C) are charged into a four-necked resin ketleast 1. It is apparentthat each chain must contain at 1 i d as i E l 3 Th reaction mixture i.least three structural units, and that the average value 15 stirredonst tl under a it atmosphere f a, b and c f R, R2 a R3 must be a least3- In t throughout the run. The reaction mixture is heataed to chains ofthis class of polyesters, the ratio of b to c is 180C where thetemperature is h ld f 10 h D approximately 1:1. Since the p-oxybenzoylmoiety of ing this period, the cyanuric chloride reacts with the FormulaII is capable of forming blocks of repeating pcopolyester to produce abranched polyester, I-ICI oxybenzoyl units in such chains, the ratio ofa:b:c may being liberated. The resulting polyester suspension is be ashigh as about 10:1:1, but since the moieties of cooled to roomtemperature, acetone is added, and the Formulas III and IV are capableof forming chains in polyester is recovered by filtration, washed withacewhich such moieties alternate and form repeating tone and dried invacuum at 110C for 2 hours. The blocks, the ratio of a:b:c may be as lowas about product is a branched polyester having Formula XXII 1:10:10.wherein R", R and R have the above-described Preferably the ratio ofa:b:c is about 12111. In this meaning; the dicarbonyl moiety isisophthaloyl; the dicase, the three moieties are capable of linking ineither oxyarylene moiety is p-dioxyphenylene; the ratio of pof twosequences, represented by Formulas XX and oxybenzoyl units toisophthaloyl units to p- XXI dioxyphenylene units is about 1:1:1; andthe number of ft a ie h l. L J11 l (XXI) int it I @i or 1. o

wherein X, m and n have the above-described meanpoxybenzoyl,isophthaloyl and p-dioxyphenylene units ings. Accordingly, thepolyesters wherein the ratio of in R, R and R averages about 30.

:b: is bout 1:1:1 co r s 0 dt F l XII a c a. repn o ormua EXAMPLEIOY N138 g. 1 mole) of p-hydroxybenzoic acid, 170 g. (XXII) (1.25 moles) ofphenyl acetate and 39.75 g. (0.125 mole) of diphenyl isophthalate areplaced in a four- N\ N necked resin kettle equipped as in Example 3. Themix- \CZRIB ture is heated to 180C, and HCl is then bubbled through theresulting melt for 8 hours, during which the wherein R, R and Rindependently consist essenai ggf g gi i ggge g lg i g fi g: of one ormore groups F XX or one or hydroxybenzoate is produced thereby. TheI-ICl flow is groups Formula XXI W ma] number discontinued, and 30.6 g.(0.250 mole) of hydroquioxybenzoyl dloxyarylene and Sophthaloyl ortereph' none and 500 g. of a polyaromatic ether heat transfer thaloylunits of from 3 to about 40 in each of R R medium (by above 400C) areadded The tempera and ture is then raised to 280C where it is held for 1hour,

Branched polyesters containing each of the three raised to 300C where itis held for 2 hours, and raised moieties are conveniently prepared byfirst condensing to 320C where it is held for 5 hours. The mixture isreactants 0f Formulas VI, VII and VIII in the desired cooled and acetoneis added. The product is recovered proportions to form a linearcopolyester containing the by filtration, washed with acetone, extractedwith acethree moieties in the desired proportions, and then retoneovernight in a Soxhlet extractor, and dried in vacacting the linearcopolyester with about one-third of its uum at l 10C. The product is alinear copolyester conmolar amount of cyanuric chloride to producebranchsisting essentially of moieties of Formulas II, III and IV ing.Example 9 illustrates the preparation of a preferred in a ratio of about8:1:1, wherein the moiety of Formula branched polyester containing thethree moieties in a III is isophthaloyl and the moiety of Formula IV isparadioxyphenylene, and the average number of moieties in thecopolyester chain is about l0.

The linear copolyester is reacted with about onethird of its molaramount of cyanuric chloride, in substantial accordance with theprocedure of Example 9, to produce a branched polyester of Formula Iwherein the moiety of Formula III is isophthaloyl and the moiety ofFormula IV is para-dioxyphenylene, the ratio of a:b:c is about 8:121,and a b c is about 10, the polyester chains containing blocks ofrepeating poxybenzoyl units. 7

These branched polyesters containing each of the three moieties ofFormulas II, III and IV, as exemplified by thoseproduced in Examples 9and 10, are especially useful as thermosetting polyesters, since theymay-be cured by heating at a sufficiently high temperature, preferablyabove 300C, to cause cross-linking to occur, whereby an extremelythermally stable crosslinked polyester is produced. Such cross-linkingpresumably occurs by ester-ester interchange.

Still another particularly desirable class of branched aromaticpolyesters accordingto the invention comprises those polyesters ofFormula I wherein each chain attached to the cyanuryl nucleus (i.e., R,R and R lacks the p-oxybenzoyl moiety of Formula II and contains from 1to about 20 of each of the moieties of Formulas III and IV, the ratio ofthese two being about 1:1. Such polyesters are represented by Formula Iwherein a is 0,.b and c are each an integer from 1 to about 20, and theratio of b:c is about 1:]. In chains containing more than one unit ofeach moiety, the moieties of Formolding compounds from which shapedarticles may be formed by conventional techniques.

Such branched polyesters may readily be produced by the condensation ofcompounds of Formulas VII and VIII to form a linear polyester, andreaction of the linear polyester with about one-third of the molaramount thereof of cyanuric chloride to produce branching. It will beunderstood that the chains attached to the cyanuric nucleus may have asthe final moiety an isophthaloyl or terephthaloyl moiety, or adioxyarylene moiety. Accordingly, the terminal groups of the chainscorrespond respectively to R or R of the compound of Formula VII or to Ror R of the compound of Formula VIII. Therefore, the branched polyestersof Formula XXIII may correspond to Formulas XXIV or XXV mula IIIalternate with the moieties of Formula IV. The

polyesters of this class have the structure of Formula XXIII (XXIII)wherein i, j and k independently are integers from 1 to about 20 and X,m and n have the above-described meanings. Such polyesters are useful,for example, as

wherein R is a terminal group selected from the group consisting ofhydrogen, lower alkyl, benzyl, phenyl, and phenyl wherein one or morehydrogens are replaced by halogen or lower alkyl; R is a terminal groupselected from the group consisting of lower alkanoyl, benzoyl, andhydrogen; and X, m, n, i,j and k have the abovedescribed meanings.

Example 11 illustrates the preparation of a prepolymer of this class ofbranched polyesters.

duce, as the principal product, p-hydroxyphenyl phenyl isophthalate,i.e., an ester of the formula EXAMPLE 13 O L 440 g. (4 moles) ofhydroquinone and 636 g. (2

moles) of diphenyl isophthalate are placed in a fournecked resin kettleequipped as in Example 3. The re- The reaction is accompanied bydistillation f 231 3' action mixture is stirred constantly under anitrogen atmoles) of phenol. The product may also contain small h e hthrehgheut the The tempereture 9 the amounts f unreacied raw materialsand/or higher com distilling head is set at 180C and the reactionmixture densation products is heated to 250C, forming a melt. Thetemperature of The temperature is reduced to 7 4 (1 the mixture is heldat 250C for 7 hours, during which mole) of cyanuric chloride is added,and the tempera- 367 of dlstltlate prhharlty Phenol, eoheetede ture isheld at 170C for 8 hours. During this period, the resultmg melt 15Poured tray and i to cool reaction mixture 'becomes a very viscous meltas a reto tooth temperature solidifying- The Sohd grouhd to sult of thereaction of the cyanuric chloride and ester 3 flhe p The Product 15 anester P- 150OC) of to produce a branched polyester prepolymer. 5 theformula The melt is'hcated to 210C to reduce its viscosity, O O pouredinto a tray and allowed to cool to room temperll IL ature, solidifying.The solid is ground to a fine powder. Q (hon on A yield of 1,093 g.(near theoretical) is obtained. The product consists primarily of abranched polyester prepolymer corresponding to Formulas XXlll and XXlVwherein n is'O; the dicarbonyl moiety is isophthaloyl; Aibranchedpolyester is P p from t ester y the dioxyaryiene moiety isparadioxyphenyiemg; i j mixing the ester in a heat transfer medium, DOW-and k are h 1; and is phenyi THERM A, heating the mixture to 190C, andgradu- Prepolymers such as that produced in Example 11 any addingOne-third mole of cyanuric Chloride P may be cured by cross-linking toproduce thermoset mole of the ester- Thereby is Produced a p p ypolyesters having outstanding thermal stability. This eerreshehdihg t0Formula XXV wherein R16 is yd may be accomplished by heating theprepolymer with gen; 1S 0; "J and k are each 1; the dleat'bohyl meletyan aromatic dihydroxyl compound to a temperature isephthuloyl; and thedtexyill'ylehe is P sufficient to produce cross-linking. Suchcross-linking yp y is illustrated in Example 12 the cross-linking agentPrepolymers such as that produced in Example 13 being the linearcopolyester produced in Example 3. may be cured by cross-linking withadditional cyanuric chloride to produce highly cross-linked polyesterspos- EXAMPLE l2 sessing marked thermal stability. The cross-linking may4 g. of the linear copolyester produced in Example 3 be effected bysuspending the prepolymer in a suitable and l g. of the branchedpolyester prepolymer proliquid heat transfer medium with about one-thirdmole duced in Example 1.1 are blended and spread on the of cyanuricchloride per mole of prepolymer, and heatsurface of a hot plate. Thetemperature of the hot plate ing to a sufficiently high temperature,preferably about is gradually increased. At about 250C the mixturel180C. The product is a cross-linked polyester forms a melt, which isthen continually agitated with 40 consisting essentially ofstructuralunits having Formula spatula as the temperature continues to rise to350C. XXVI (XXVI) The temperature is held at 350C,with continuedagitawherein X, m and n have the above-described meantion. When most ofthe volatiles have been dissipated, ings. Cross-linking the prepolymerproduced in Examagitation isdiscontinued and the melt is spread out intople l3 inthis manner produces a cross-linked polyester a film f e atotal time f'abO 1 hour a thin. fi consisting essentially of structuralunits having Formula strong, transparent film is formed consistingessentially XXVI wherein n is 0, the dioxyarylene moieties are pofthermoset cross-linked polyester. The cross-linking dioxyphenylene, andthe dicarbonyl moieties are isophpresumably occurs initially bycondensation between thaI L the te m na y y g p f the linear copolyesterExample 14 illustrates the preparation of a branched and the terminalphen xy group of the branched P polyester wherein the chains consistessentially of alterpolymer, and subsequently by ester-ester interchangemating i i f F l III d IV,

reactions. I

Example 13 illustrates the preparation of another EXAMPLE I4 prepolymer,corresponding to Formula XXV. 954 g. '(3moles) of diphenyl isophthalate,363 g. (3.3

throughout the run. The mixture is heated to 250C,

then heated from 250 to 300C at a rate of C/hour, and finally held at300C until approximately the theoretical amount of phenol (564 g.) forcomplete condensation has distilled off (about hours). The product ofthe condensation reaction is a linear polyester corresponding to theformula wherein the average value of p is about 10. The polyester chainsterminate at each end with a dioxyphenylene moiety by virtue of themolar excess of hydroquinone employed, the extent of such excessregulating the average value of p.

The temperature is reduced to 180C, 18.4 g. (0.1 mole) of cyanuricchloride is added, and the temperature is maintained at 180C for 10hours, during which the cyanuric chloride and linear copolyester reactto produce a branched polyester, HCl being liberated. The resultingbranched polyester suspension is cooled to 80C and acetone is added. Thepolyester'is removed by filtration, washed with acetone, and dried invacuum at 1 10C for 2 hours. The product is a branched polyestercorresponding to Formulas XXXlll and XXV wherein n is 0; the average ofi,j and k is about 10; the dicarbonyl moiety is isophthaloyl; thedioxyarylene moiety is p-dioxyphenylene; and R is hydrogen.

While the invention has been described herein with reference to certainexamples and preferred embodiments, it is to be understood that variouschanges and modifications may be made by those skilled in the artwithout departing from the concept of the invention, the scope of whichis to be determined by reference to the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A branched aromatic polyester of Formula I wherein a, b and c beingintegers representing the total number of the respective moieties ineach of R, R and R wherein:

i i X 15 -O-I or II o nis0or1,andwhennis1,mis0orl;

the carbonyl groups of the moiety of Formula 111 are meta or para toeach other;

the oxy groups of the moiety of Formula IV are meta or para to eachother;

wherein:

the oxy groups of the moieties of Formulas II and IV are linked to acarbonyl group of a moiety of Formulas 11 or III or to a carbon-atom ofthe cyanuryl nucleus;

the carbonyl groups of the moieties of Formulas I1 and III are linked toan oxy group of a moiety of Formulas 11 or IV;

the carbon atoms of the cyanuryl nucleus are linked to an oxy group of amoiety of Formulas II or 1V;

' and wherein:

a is an integer from 0 to about 40;

b is an integer from 0 to about 20;

c is an integer from 0 to about 20;

a b c is an integer from 2 to about 40;

the average value of a, b and c for R, R and R is from 2 to about 40;

when a is 0, b is an integer from 1 to about 20 and c is an integer from1 to about 20;

when b is 0, a is an integer from 1 to about 40 and c is 0 or 1 whenband c are each 0, a is an integer from 2 to about 40. g

2. A branched aromatic polyester as set forth in claim 11 of the formulaN c C-EOQ. 1- 11 a N\ & o

wherein the bracketed portions represent repeating poxybenzoylstructural units and d, e and f independently are integers from 2 toabout 40.

3. A branched aromatic polyester prepolymer as set forth in claim 2wherein d, e andfindependently are integers from 2 to about 10.

4. A cross-linked polyester produced by heating a branched aromaticpolyester prepolymer as set forth in claim 3 with a suitablecross-linking agent selected from the group consisting of aromaticdihydroxy compounds, aromatic dicarboxylic acids, low molecular weightpolyesters containing aromatic structural units derived from suchdihydroxy compounds and/or dicarboxylic acids, and cyanuric halide, at atemperature sufficiently high to cause cross-linking.

5. A branched aromatic polyester as set forth in claim 1 wherein b is 0,c is l, and a is an integer from 1 to about 40.

6. A branched aromatic polyester prepolymer as set forth in claim 5wherein a is 2.

7. A branched aromatic polyester prepolymer as set forth in claim 5whereina is l.

8. A branched aromatic polyester prepolymer as set forth in claim 5wherein n is O.

9. A branched aromatic polyester prepolymer as set forth in claim 8wherein a is 2.

10. A branched aromatic polyester prepolymer as set forth in claim 8wherein a is l.

11. A branched aromatic polyester prepolymer as set forth in claim 1 ofthe formula wherein R has the formula and wherein R represents theterminal group and is selected from the group consisting of loweralkanoyl, benzoyl and hydrogen.

15. A branched aromatic polyester prepolymer as set forth in claim 14wherein n is 0.

16. A branched aromatic polyester prepolymer as set forth in claim 15wherein R is hydrogen.

17. A cured polyester produced by heating a prepolymer as set forth inclaim 11 at a temperature above its melting point.

18. A cross-linked polyester consisting essentially of structural unitshaving the formula wherein R represents the terminal group and is se- 0lected from the group consisting of lower alkanoyl, benzoyl andhydrogen.

12. A branched aromatic polyester prepolymer as set forth in claim 11wherein n. is 0.

13. A branched aromatic polyester prepolymer as set 65 forth in claim 12wherein R is hydrogen.

14. A branched aromatic polyester prepolymer as set forth in claim 1 ofthe formula N N wherein:

L l n I n w e e R has h formula n is or 1, and when n is 1, m is 0 or 1.

27. A branched aromatic polyester as set forth in claim 26 wherein n is0. 28. A cured polyester produced by heating a o d o branched aromaticpolyester as set forth in claim 22 at a sufficiently high temperature tocause cross-linking. 29. A branched aromatic polyester as set forth inclaim 1 wherein a is 0, b is an integer from 1 to about 20, c is aninteger from 1 to about 20, and b.'c is about 1:1.

30. A branched aromatic polyester as set forth in claim 29 wherein n is0. O O 31. A branched aromatic polyester as set forth in claim 1 havingthe structure wherein: X is nisOor 1,andwhennis 1,mis0or l. 21. Across-linked polyester as set forth in claim 20 A 11 t1 wherein n [S 0.3L0+ -K X)... %"/O 22. A branched aromatic polyester as set forth in N Nclaim 1 wherein a, b and c are each at least 1; a b V n V l c is aninteger from 3 to about 40; the average value of I I 0 a, b and c for R,R and R is from 3 to about 40; the L. -O T {pH- ild? ratio ofa:b:c isfrom about 1:10:10 to about 10:1 :1; and I the ratio of [1:0 is about1:1. X/ V V 23. A branched aromatic polyester as set forth in claim 22wherein the ratio of a:b:c is about 1:1:1. herein 24. A branchedaromatic polyester as set forth in X is claim 22 wherein n is 0.

25. A branched aromatic polyester as set forth in 0 claim 23 wherein nis 0. l Al 26. A branched aromatic polyester as set forth in II claim 1of the formula nisOorl,andwhennisl,mis0orl;

N and i, j and k independently are integers from 1 to H In about 20. R32. A branched aromatic polyester as set forth in claim 31 wherein n is0.

04m 33. A branched aromatic polyester prepolymer as set forth in claim31 wherein i,j and k are each 1.

34. A branched aromatic polyester prepolymer as set wherein R", R and Rindependently consist essenforth in claim 33 wherein n is 0. tially ofone or more groups of the formula 35. A branched aromatic polyester asset forth in ff/ (M t 1 i1 --o X'... 0- o c 1 sh \1/ 3 1 n or one ormore groups of the formula claim 1 of the formula s 1L0} l 1 Q gs @1 28wherein i,j and k independently are integers from 1 to about and R is aterminal group selected from the group consisting of lower alkanoyl,benzoyl and hydrogen.

wherein L and k independently are integers from 1 to wherein: about 20and R is a terminal group selected from the X is ,250/6 group consistingof hydrogen, lower alkyl, benzyl, phenyl, and phenyl wherein one or morehydrogens are replaced by halogen or lower alkyl.

36. A branched aromatic polyester as set forth in claim wherein n is 0.

37. A branched aromatic polyester as set forth in claim 36 wherein R isphenyl. 35

38. A branched aromatic polyester prepolymer as set W H forth in claim35 wherein i, j and k are each 1 and n is 0.

39. A cured polyester produced by heating a prepolymer as set forth inclaim 38 with an aromatic dihy- 40 droxyl compound to a sufficientlyhigh temperature to produce crossqinking n is O or 1, and when n 1s 1, mis 0 or 1.

40. A branched aromatic polyester s set f rth i 44. A cross-linkedpolyester as set forth in claim 43 claim 1 of the formula wherein n is0.

xypg/ on mm? oR pom-E 01m /ll o o .MLJ 01. \g

1. A BRANCHED AROMATIC POLYESTER OF FORMULA I
 2. A branched aromaticpolyester as set forth in claim 1 of the formula
 3. A branched aromaticpolyester prepolymer as set forth in claim 2 wherein d, e and findependently are integers from 2 to about
 10. 4. A cross-linkedpolyester produced by heating a branched aromatic polyester prepolymeras set forth in claim 3 with a suitable cross-linKing agent selectedfrom the group consisting of aromatic dihydroxy compounds, aromaticdicarboxylic acids, low molecular weight polyesters containing aromaticstructural units derived from such dihydroxy compounds and/ordicarboxylic acids, and cyanuric halide, at a temperature sufficientlyhigh to cause cross-linking.
 5. A branched aromatic polyester as setforth in claim 1 wherein b is 0, c is 1, and a is an integer from 1 toabout
 40. 6. A branched aromatic polyester prepolymer as set forth inclaim 5 wherein a is
 2. 7. A branched aromatic polyester prepolymer asset forth in claim 5 wherein a is
 1. 8. A branched aromatic polyesterprepolymer as set forth in claim 5 wherein n is
 0. 9. A branchedaromatic polyester prepolymer as set forth in claim 8 wherein a is 2.10. A branched aromatic polyester prepolymer as set forth in claim 8wherein a is
 1. 11. A branched aromatic polyester prepolymer as setforth in claim 1 of the formula
 12. A branched aromatic polyesterprepolymer as set forth in claim 11 wherein n is
 0. 13. A branchedaromatic polyester prepolymer as set forth in claim 12 wherein R4 ishydrogen.
 14. A branched aromatic polyester prepolymer as set forth inclaim 1 of the formula
 15. A branched aromatic polyester prepolymer asset forth in claim 14 wherein n is
 0. 16. A branched aromatic polyesterprepolymer as set forth in claim 15 wherein R11 is hydrogen.
 17. A curedpolyester produced by heating a prepolymer as set forth in claim 11 at atemperature above its melting point.
 18. A cross-linked polyesterconsisting essentially of structural units having the formula
 19. Across-linked polyester as set forth in claim 18 wherein n is
 0. 20. Across-linked polyester consisting essentially of structural units havingthe formula
 21. A cross-linked polyester as set forth in claim 20wherein n is
 0. 22. A branched aromatic polyester as set forth in claim1 wherein a, b and c are each at least 1; a + b + c is an integer from 3to about 40; the average value of a, b and c for R1, R2 and R3 is from 3to about 40; the ratio of a:b:c is from about 1: 10:10 to about 10:1:1;and the ratio of b:c is about 1:1.
 23. A branched aromatic polyester asset forth in claim 22 wherein the ratio of a:b:c is about 1:1:1.
 24. Abranched aromatic polyester as set forth in claim 22 wherein n is
 0. 25.A branched aromatic polyester as set forth in claim 23 wherein n is 0.26. A branched aromatic polyester as set forth in claim 1 of the formula27. A branched aromatic polyester as set forth in claim 26 wherein n is0.
 28. A cured polyester produced by heating a branched aromaticpolyester as set forth in claim 22 at a sufficiently high tempErature tocause cross-linking.
 29. A branched aromatic polyester as set forth inclaim 1 wherein a is 0, b is an integer from 1 to about 20, c is aninteger from 1 to about 20, and b:c is about 1:1.
 30. A branchedaromatic polyester as set forth in claim 29 wherein n is
 0. 31. Abranched aromatic polyester as set forth in claim 1 having the structure32. A branched aromatic polyester as set forth in claim 31 wherein n is0.
 33. A branched aromatic polyester prepolymer as set forth in claim 31wherein i, j and k are each
 1. 34. A branched aromatic polyesterprepolymer as set forth in claim 33 wherein n is
 0. 35. A branchedaromatic polyester as set forth in claim 1 of the formula
 36. A branchedaromatic polyester as set forth in claim 35 wherein n is
 0. 37. Abranched aromatic polyester as set forth in claim 36 wherein R15 isphenyl.
 38. A branched aromatic polyester prepolymer as set forth inclaim 35 wherein i, j and k are each 1 and n is
 0. 39. A cured polyesterproduced by heating a prepolymer as set forth in claim 38 with anaromatic dihydroxyl compound to a sufficiently high temperature toproduce cross-linking.
 40. A branched aromatic polyester as set forth inclaim 1 of the formula
 41. A branched aromatic polyester as set forth inclaim 40 wherein n is
 0. 42. A branched aromatic polyester prepolymer asset forth in claim 41 wherein i, j and k are each 1 and R16 is hydrogen.43. A cross-linked polyester consisting essentially of structural unitsof the formula
 44. A cross-linked polyester as set forth in claim 43wherein n is 0.